1. Field of the Invention
The present invention relates to a numerical control method capable of performing various controls at high speeds, with a desired positioning accuracy.
2. Description of the Related Art
In positioning control effected by a numerical control apparatus, a control object is controlled so that a deviation between a target position and an actual position falls within a predetermined range. In machining a workpiece, for instance, the numerical control apparatus reads, block by block, an NC program in which machining conditions such as a tool locus are stated, and executes respective blocks of the program in sequence. In the case of the thus read block containing a moving command, the numerical control apparatus determines completion of positioning control for a block when the absolute of a stored value of an error register, housed in a servo circuit which forms part of a tool driving system, reaches a value below a preset in-position value during the execution of the same block. The numerical control apparatus then starts the execution of the next block, the stored value representing a deviation or error between a target moving amount of a tool, specified by the moving command, and an actual moving amount of the tool detected by a position detector.
In a positioning control of this kind, the positioning accuracy is improved but a period of time required for positioning is lengthened as the in-position value is set to a smaller one.
According to the conventional method, the in-position value is fixedly set, and hence it is difficult to simultaneously obtain an improved positioning accuracy and a shortened execution time period for desired positioning.